The present disclosure relates to subject matter contained in priority Japanese Patent Application No. 2001-354209, filed on Nov. 20, 2001, the contents of which is herein expressly incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a DCxe2x80x94DC conversion switching power supply, and more particularly relates to a switching power supply including a plurality of DCxe2x80x94DC converters connected in parallel.
2. Description of Related Art
It has been known that a plurality of switching power supplies, or DCxe2x80x94DC converters therefor are connected in parallel to increase their efficiency as well as to decrease the size and weight of a DCxe2x80x94DC conversion switching power supply for supplying medium or high power. Recently, in particular, a type called the xe2x80x9cinterleave typexe2x80x9dxe2x80x94which displaces the phase of a switching current of the switching power supplies, or the DCxe2x80x94DC converters, connected in parallel to one anotherxe2x80x94is often used to decrease the effective value of an input current, thereby increasing efficiency.
FIG. 34 shows a conventional interleave type switching power supply including triple parallel circuit constitution. In this drawing, the reference numerals 1a, 1b, and 1c respectively denote first, second, and third DCxe2x80x94DC converters, while the reference numerals 1ai, 1bi, and 1ci respectively denote switching current signals of the DCxe2x80x94DC converters 1a, 1b, and 1c. The reference numeral 2 denotes a current mode control circuit, while the reference numerals 21a, 21b, and 21c respectively denote first, second, and third comparators, and the reference numerals 21ao, 21bo, and 21co respectively denote output pulses from the comparators 21a, 21b, and 21c. The reference numeral 22 denotes a detection signal control circuit, while the reference numeral 22o denotes a control voltage of the detection signal control circuit 22. The reference numeral 3 denotes a DC power supply, and 4 denotes a load. While a phase delay circuit for the switching current (which displaces the phases of the switching current of the DCxe2x80x94DC converters 1a, 1b, and 1c) is required for the interleave, details of the phase delay circuit are not necessary for describing this part of the apparatus and are omitted from this drawing.
The current mode control circuit 2 uses the detection signal control circuit 22 to detect output voltages, or output currents, from the DCxe2x80x94DC converters 1a, 1b, and 1c connected in parallel. This creates a controlling output voltage 22o which is compared with the switching current signals 1ai, 1bi, and 1ci respectively by the comparators 21a, 21b, and 21c. This results in the individual output pulses 21ao, 21bo, and 21co. These output pulses 21ao, 21bo, and 21co are then used to control operation such that the peaks of the switching current signals 1ai, 1bi, and 1ci of the respective DCxe2x80x94DC converters 1a, 1b, and 1c are equal to the control voltage 22o. As a result, the output voltages or currents from the DCxe2x80x94DC converters 1a, 1b, and 1c are controlled so as to be constant.
FIG. 35A shows the basic waveforms of the control voltage 22o, the switching current signals 1ai, 1bi, and 1ci, and the output pulses 21ao, 21bo, and 21co. However, a spike current, and an in-circuit resonance current, flow in the DCxe2x80x94DC converters 1a, 1b, and 1c every time the switching current turns on or off. These DCxe2x80x94DC converters 1a, 1b, and 1c, and the current mode control circuit 2, are connected to each other at several points including: a detection input of the detection signal control circuit 22; the input for the switching current signals 1ai, 1bi, and 1ci of the comparators 21a, 21b, and 21c; lines for the output pulses 21ao, 21bo, and 21co, and the line for 0V (or ground). As a result, the spike current and the in-circuit resonance current generated in the DCxe2x80x94DC converters 1a, 1b, and 1c, when turning on and off, can flow into the current mode control circuit 2 through these connection loops.
In addition, when the DCxe2x80x94DC converters 1a, 1b, and 1c, or circuits for driving a switch in the DCxe2x80x94DC converters (1a, 1b, and 1c), are provided on the same printed circuit board as the current mode control circuit 2, if their locations and connections are close to one another, the spike current and the in-circuit resonance current generated in the DCxe2x80x94DC converters 1a, 1b, and 1c are often superimposed on signals in the current mode control circuit 2 as a ripple noise, due to electromagnetic induction or the like.
The spike current flowing into the current mode control circuit 2, and the ripple noise superimposed on the signals in the current mode control circuit 2, can be considerably reduced by the connection method and the arrangement of the circuits. However, it is difficult to completely eliminate these effects, and they can also be superimposed on the control voltage 22o as a ripple noise.
If this is the case, a malfunction can result where the output pulses 21ao, 21bo, and 21co become narrower than their normal pulse width. This is shown in FIG. 35B. The control voltage 22o, on which the ripple noise is superimposed, acts as a switch-on noise or a ripple potential, resulting in a decrease in the control voltage 22o. More specifically, when the decrease in the control voltage 22o, due to the noise and ripples caused by the turning on and off of the switching current of the other DCxe2x80x94DC converters, occurs within the range of the normal pulse width of the DCxe2x80x94DC converter, the peaks of the switching current signals 1ai, 1bi, and 1ci are compared with the decreased control voltage 22o. As a consequence, the width of the output pulses 21ao, 21bo, and 21co decreases.
Additionally, since the detection signal control circuit 22 controls the output voltage or current so as to be constant, narrow pulses caused by malfunction (as above), and wide pulses compensating decreases of the output voltage or current caused by the malfunction, become mixed. The resulting state from this mixing changes depending on conditions of: the input voltage 3 and the load 4; input/output filter parameters in the DCxe2x80x94DC converters 1a, 1b, and 1c; and the response speed of the detection signal control circuit 22. Consequently, the ripple component of the output voltage or current fluctuates largely and irregularly compared with the current and voltage characteristics of normal operation. Also, since a switching current with different peaks irregularly flows in inductor components, such as a transformer or a choke in the DCxe2x80x94DC converters 1a, 1b, and 1c, mechanical vibration from gaps in a core, or from insulation tape between windings, generates noise.
As described above, when the plurality of DCxe2x80x94DC converters connected in parallel for a conventional interleave construction are controlled by a single current mode control circuit, the width of the controlling output pulses become narrower due to noise and ripples superimposed on the control voltage 22o by the spike current and in-circuit resonance current generated when the switching current in the other DCxe2x80x94DC converters turns on and off. As a result, the ripple component of the output voltage or current fluctuates significantly and irregularly. As a consequence, inductor components in the DCxe2x80x94DC converters, such as the transformer and choke, generate noise.
In light of the foregoing, an object of the present invention is to provide an interleave type switching power supply which does not generate the malfunction caused by fluctuations of the pulse width, the ripple fluctuation of the output voltage or current, and the noise from the inductor components in the DCxe2x80x94DC converters under the current mode control-with the interleave constitution.
A switching power supply of the present invention includes: a current mode control circuit for controlling a switching current pulse by comparing a switching current signal or a signal proportional to the switching current signal with a control voltage; a plurality (N) of DCxe2x80x94DC converters connected in parallel and controlled by the current mode control circuit; and an N-times frequency waveform generation circuit for generating a waveform with a frequency N times of an oscillation frequency of the DCxe2x80x94DC converters in sync with this oscillation frequency, to superimpose it on the control voltage.
With the constitution above, since superimposing the output from the N-times frequency waveform generation circuit on the control voltage practically increases the control voltage substantially having been decreased by the superimposed noise and ripple, the malfunction caused by the fluctuations of the pulse width is not generated in the current mode control with the interleave constitution, and thus, an interleave type switching power supply which does not generate the ripple fluctuation of the output voltage or current and the noise from the inductor components is constituted.
In addition, the output of the N-times frequency waveform which is generated by the N-times frequency waveform generation circuit, and is superimposed on the control voltage can be in phase with the turning-on phase of the switching current signal or a signal in phase with the switching current signal.
On the other hand, when the output of the N-times frequency waveform which is generated by the N-times frequency waveform generation circuit, and is superimposed on the control voltage is in phase with the turning-off phase of the switching current signal or a signal in phase with the switching current signal, the actions and the effects above are provided even when a change in the pulse width is large.
Further, when the output of the N-times frequency waveform which is generated by the N-times frequency waveform generation circuit, and is superimposed on the control voltage is in phase with a phase arbitrarily delayed from the turning-on phase or turning-off phase of the switching current signal or a signal in phase with the switching current signal, the actions and the effects above are also provided even when the change in the pulse width is large.
Additionally, the switching power supply may include the current mode control circuit described above, two DCxe2x80x94DC converters connected in parallel and controlled by the current mode control circuit, and a twice-frequency waveform generation circuit for generating a waveform with a frequency twice of an oscillation frequency of the DCxe2x80x94DC converters in sync with this oscillation frequency, and simultaneously in phase with the turning-on phase or turning-off phase of the switching current signal or a signal in phase with this switching current signal, to superimpose it on the control voltage. Here the twice-frequency waveform generation circuit may serve as a slope compensation circuit. This restrains a decrease of the control range largely, and thus avoids a decrease of the input/output range caused by the addition of the slope compensation compared with a case where a slope compensation waveform is added to the switching current signal.
In addition, the switching power supply may include the current mode control circuit described above, a plurality (N) of DCxe2x80x94DC converters connected in parallel and controlled by the current mode control circuit, and a next phase synchronized waveform generation circuit for generating a voltage waveform starting from the turning-on phase of the switching current signal of a (K+1)th DCxe2x80x94DC converter or a signal in phase with this switching current signal, and rising as time elapses, to superimpose this voltage waveform on the switching current signal or the signal proportional to the switching current signal of a Kth DCxe2x80x94DC converter. This restrains the decrease of the control range largely, and thus avoids the decrease of the input/output range caused by the addition of the slope compensation even under a condition requiring the slope compensation.
Further, the switching power supply may include the current mode control circuit and the DCxe2x80x94DC converters described above, and a (xcex4=0.5) synchronized waveform generation circuit for generating a voltage waveform starting from a phase delayed by 0.5 of an on-time ratio (xcex4) from the turning-on phase of the switching current signal of the DCxe2x80x94DC converter or a signal in phase with this switching current signal, and rising as time elapses, to superimpose this voltage waveform on the switching current signal or the signal proportional to the switching current signal of the DCxe2x80x94DC converts. This restrains the decrease of the control range largely even further, and thus avoids the decrease of the input/output range caused by the addition of the slope compensation even under the condition requiring the slope compensation.
Additionally, the switching power supply may include the current mode control circuit, the DCxe2x80x94DC converters, the N-times frequency waveform generation circuit for generating a waveform with a frequency N times of an oscillation frequency of the DCxe2x80x94DC converters in sync with this oscillation frequency, to superimpose it on the control voltage, and an on/off circuit for switching the N-times frequency waveform generation circuit between on and off. This makes it possible to turn off the superimpose of the N-times frequency waveform so as to smoothly conduct constant current transition without the malfunction caused by the superimpose if a constant current control is applied to a load such as a battery.
In addition, the switching power supply may include the current mode control circuit, the DCxe2x80x94DC converters, the N-times frequency waveform generation circuit for generating a waveform with a frequency N times of an oscillation frequency of the DCxe2x80x94DC converters in sync with this oscillation frequency, to superimpose it on the control voltage, and a changing circuit for increasing/decreasing the output level of the N-times frequency waveform generation circuit. This makes it possible to smoothly change the N-times frequency waveform to be superimposed so as to smoothly conduct constant current transition without the malfunction caused by the superimpose when constant current control is applied to a load such as a battery.
Further, it is preferable to constitute the switching circuit and the variable circuit so as to operate based on detecting the on-time ratio (xcex4) of the DCxe2x80x94DC converters.
Additionally, it is preferable that the DCxe2x80x94DC converters have a bidirectional conversion function, and the current mode control circuit is switched between controlling the input and output of the DCxe2x80x94DC converters based on an external signal.
In addition, the actions and the effects above are remarkable when a load or a power supply connected with an input or output of the DCxe2x80x94DC converters is a battery.
Further, it is preferable that the output voltage waveform from the N-times frequency waveform generation circuit over one period decreases as time elapses.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.